1. Field of the Invention
The present invention relates to a continuously forming method for continuously forming a synthetic stone slab.
2. Description of the Prior Art
Heretofore, an apparatus for manufacturing a panel-like polymerized material by continuously polymerizing polymerizable compounds, has been known, as disclosed in Japanese Patent Publication No. Sho 47-84815 entitled "Continuous Polymerization Method and Apparatus therefor". For example, in an apparatus using metal endless belts as disclosed in the above-mentioned publication, two band-like metal belts which are stretched in an endless manner such as to be horizontally laid in parallel with each other with a predetermined gap therebetween, and which are sealed by gaskets at their opposite widthwise sides, are moved in one and the same direction at one and the same speed while liquid resin is continuously filled into the gap therebetween so as to continuously form a resin sheet. Further, the apparatus as mentioned above incorporates a device for generating a suitable liquid pressure between the surfaces of the metal belts so as to prevent the upper metal belt horizontally running from flexing, in order to obtain a product having an uniform thickness.
However, in the above-mentioned conventional continuous forming method, it is necessary to adjust the height of the column of a liquid material in a filling duct and the degree of depressurization in the upper space in the duct. Accordingly, complicated devices such as a vacuum generating unit and a material feed duct having a height as high as about 5 m should be provided, and in addition, adjustment to the thickness of the product has been difficult.
Another possible forming method excluding the above-mentioned device is such that resin is filled and hardened between two films laid in two layers one over another and horizontally running in parallel with each other, the lower film sliding on a support bed. This method is preferable since it does not require the above-mentioned complicated apparatus including metal belts or the like, and since it can form a sheet-like mold product with the use of a simple arrangement. However, this method has a disadvantage such that it cannot be applied for molding which requires a high degree of accuracy for its thickness.
The reason why such a degree of accuracy cannot be expected, is considered that a volume of a molding material larger than a proper volume of molding material, which is defined as the product of the area of a gap between rollers and the surface of the support bed and a film traveling speed per unit time, is transferred to pass through the gap, even though, for example, the molding material poured into between the films is fed through the rollers, and accordingly, the rollers cannot exhibit a substantial effect upon the control of the thickness. That is, it can be readily understood by taking into a consideration that the flowing speed of the molding material in the gap exceeds the film traveling speed, and accordingly, if the films are adjusted to a shape corresponding to the gap, a difference in pressure applied to the molding pressure occurs between the inlet and the outlet of the rollers.
Namely, on the inlet side of the rollers, the pressure of the molding material stagnating at least above the upper end of the roller gap causes the molding material to pass therethrough at a speed higher than the film travelling speed. Accordingly, the thus obtained thickness of the molding material is directly and greatly influenced by the level of the molding material on the roller inlet side. Further, the upper surface of the molding material humps up exceeding the upper end of the roller gap, due to the above-mentioned reason, just after it passes through the rollers, and finally, the liquid pressure of the molding material balances with a pressure which is given by the tension applied to the films and which is to confine the molding material, so that the molding material comes to be static. Thus, the molding material having passed through the rollers, bulges out in a convex shape in the cross-section as view in the travelling direction. As a result, such a disadvantage has been experienced to that a uniformly flat sheet cannot be obtained.